The evolution of broad band wireless services such as Wideband Code Division Multiple Access (WCDMA) and Long Time Evolution (LTE) has improved the performance of high linear wide band power amplifiers, normally called Multi Carrier Power Amplifiers (MCPA). The MCPA may also be used to amplify combined multiple narrow band carriers signals, such as multiple Global System for Mobile communications (GSM) carriers. The use of MCPA for GSM thus removes the need for high power radio frequency combiners.
The use of MCPA for GSM, WCDMA, LTE or other cellular radio systems requires that the allocation of radio frequency power is divided among the carrier controllers of the same MCPA. The allocation of power has to be performed in accordance with a common cell planning.
A problem with MCPA is to maintain the input signal within the linear range of the power amplifier. In a legacy broad band wireless system, the input signal is normally controlled by a single controlling entity, ensuring operation to be within range. In a GSM system with multiple GSM carriers, each with its own corresponding controlling entity, a coordination of the input signal strengths is required.
The MCPA may also be used to amplify the combined signal of carriers of different standards, such as the combination of two GSM carriers and one WCDMA carrier. A coordination of the input signal is then again required. The present invention relates to the coordination of signal strength between controlling entities, or carrier controllers, of the same or different standards.
Thus the user plane data is managed by a carrier controller. The carrier controller is a control function which, amongst other, controls the output power to be used by the carrier it controls. In this context, the carrier may be a portion of the air interface carrier as defined by the relevant standard such as e.g. 3GPP etc, the portion being characterized by having a certain traffic type and/or priority. The carrier controller may also operate on a plurality of carriers.
Each carrier controller may allocate as much radio frequency power from the MCPA as assigned, but not more. If an over-allocation occurs, the MCPA will limit the transmitted signal in some way and transmitted information will get lost or has to be re-transmitted.
Carrier controllers from different systems schedule their power allocation with different time increments, as shown in FIG. 1. In the illustrated example, the scheduling horizon for GSM, WCDMA and LTE respectively, is shown. For GSM the scheduling horizon is 1.5 ms, i.e. the time in advance the GSM base station knows which radio frequency power level a certain time slot must use with a duration of 0.5 ms. For WCDMA and LTE the radio frequency power level must be defined 2 ms before the transmission starts with a duration of 2 ms for WCDMA and a duration of 1 ms for LTE.
Existing solutions, as shown in FIG. 2, offers a static, pre-determined allocation of radio frequency power which do not take into account the short-term under-allocation of radio frequency power by other carrier controllers sharing the same MCPA which in reality offers ‘spare’ power to be used especially when GSM is introduced.
A GSM transmitter is configured for a nominal power which is the maximum power any time slot will use in that transmitter whereas some or all time slots in reality will be transmitted at a lower power than configured.
The available radio frequency power is therefore not always fully used due to the differences between configured and used power or differences between system concepts such as e.g. GSM, WCDMA and LTE as shown in FIG. 2.
A problem with the existing solution is that the potentially available radio frequency power of the MCPA is not used, which leads to a low throughput.